The present invention relates to a motor vehicle having an electric machine.
An electric power supply of a motor vehicle having hybrid drive is known from DE 10252507 A1, for example. Inter alia, super capacitors (so-called “super caps”) are disclosed in this case as the electrical power accumulators. The use of such super capacitors has the advantage that stored electrical power is transferable in a large amount in a short time from the power accumulators to an electric machine to accelerate the motor vehicle, for example.
However, precisely this advantage is a disadvantage in specific vehicle operating states, for example, in an accident situation or a repair situation. This is because in the cited situations, the rapid availability of high power represents a danger to the humans, for example, to rescue personnel or motor vehicle mechanics.
The present invention is therefore based on the object of specifying a motor vehicle having electric machine and electrical power source, whose handling is possible safely in many vehicle operating states.
This and other objects and advantages are achieved by exemplary embodiments of the present invention, in which a motor vehicle having an electrical power source, in particular a power accumulator, for providing DC current, is equipped with a converter (power converter, power inverter) for converting the DC current into three-phase AC current of identical phase angle or polyphase current as a function of the vehicle operating state, and with an electric machine, such as a polyphase machine, which is fed the current provided by the converter.
The present invention is based on the idea of discharging the power source in a controlled way in specific vehicle operating states, for example, in a vehicle operating state “accident” (accident vehicle operating state) or in a vehicle operating state “repair” (repair vehicle operating state). After the discharge of the power source, it is possible to handle the motor vehicle safely even in the cited vehicle operating states.
For the controlled discharge (safety discharge) the converter may be set up automatically in such a way in critical vehicle operating states that it outputs—not polyphase current as in normal vehicle operating states, but rather—three-phase AC current of identical phase angle to the electric machine. Components of the electric machine are thus used in the cited vehicle operating states to “dispose of” the power provided by the power source, for example. Separate discharge resistors or discharge circuits provided for this purpose, as are required in guidelines of electrical engineering, for example, may thus be dispensed with. Weight and installation space may thus be saved.
The motor vehicle advantageously includes a control unit, which is set up to control the converter in such a way that the converter automatically provides three-phase AC current of identical phase angle or polyphase current as a function of a current vehicle operating state. In particular, the control unit may be set up in such a way that the converter automatically provides three-phase AC current of identical phase angle and/or feeds the electric machine upon the presence of a critical vehicle operating state and automatically provides polyphase current in other or normal vehicle operating states.
To efficiently “dispose of” the DC current power provided by the power source in the electric machine or convert it into heat, a converter is provided that is set up in such a way in specific vehicle operating states that instead of polyphase current (three-phase AC current of differing phase angle), three-phase AC current of identical phase angle is output by the converter in these vehicle operating states. Therefore, essentially no rotating field is generated in the electric machine. Instead, an alternating field is applied to the windings of the electric machine, and the power provided is thus degraded by unfavorable operation of the electric machine, essentially without generating a torque. The electric machine is thus intentionally not driven in the cited, particularly critical vehicle operating states, but rather is only used for “power disposal.”
In an exemplary embodiment of the present invention, the control unit is set up in such a way that the converter automatically provides three-phase AC current of identical phase angle or feeds the electric machine upon the existence of a critical vehicle operating state and upon detecting a current vehicle velocity which falls below a predefined limit velocity, in particular upon detecting a current vehicle velocity of 0 km/h. A safety discharge of the power source as described above may thus reliably be prevented from occurring during normal travel, which could result in damage to the engine and/or the transmission.
The electric power source is, for example, a super capacitor, a motor vehicle battery, or a fuel cell, which may cause the propulsion of the vehicle.
A detection unit, which feeds the detected current vehicle operating state to the control unit, may be provided for detecting the current vehicle operating state.
In an exemplary embodiment of the present invention, the detection unit includes an acceleration sensor, the detection unit being set up in such a way that it may detect an accident vehicle operating state, in particular if the detected acceleration exceeds a predefined threshold value. A safety discharge via the electric machine as explained above may thus be triggered.
An input interface, which feeds the input current vehicle operating state to the control unit, may be provided for inputting the current vehicle operating state.
In an exemplary embodiment of the present invention, the input interface is set up in such a way that a repair vehicle operating state may be input via the input interface, so that a safety discharge via the electric machine as explained above may thus also be triggered.
The motor vehicle, in particular as a hybrid vehicle, is advantageously drivable by the electric machine and/or the power source is chargeable by the power of the motor vehicle and/or based on an internal combustion engine of the motor vehicle.
The present invention has been shown to be especially advantageous if the power source has one, multiple, or all of the following three properties:
discharge time of the power source is less than 20 seconds;
power content of the power source is greater than 100 watt-hours;
the rated voltage of the power source is greater than 60 volts.
This is because the handling of a motor vehicle in the cited critical vehicle operating states is especially hazardous when power sources of this type are used and/or rapid and reliable discharge of the power source in the cited critical vehicle operating states without knowledge of the present invention is especially complex.
In an exemplary embodiment of the present invention, the power source includes a fuel cell fed from a hydrogen tank, the control unit for controlling the converter being set up in such a way that the converter automatically provides three-phase AC current of identical phase angle or polyphase current as a function of the state of the hydrogen tank, in particular the pressure conditions in the tank. In particular, three-phase AC current of identical phase angle is automatically provided or fed to the electric machine if the pressure in the hydrogen tank exceeds a predefined limiting pressure, or if the so-called boil-off state, in which hydrogen must be bled in a controlled way from the tank for safety reasons, is detected or imminent.
Instead of bleeding hydrogen from the hydrogen tank, in this embodiment, power is disposed of in a controlled way, which is fed for this purpose to the electric machine as three-phase AC current of identical phase angle via the converter. The converter is powered with electrical power, in particular DC current, by the fuel cell. The fuel cell consumes hydrogen from the hydrogen tank for this purpose, so that the cited limiting pressure is not exceeded, and/or the boil-off state does not occur or is delayed. The boil-off state of the hydrogen tank may also be considered a critical vehicle operating state. In normal vehicle operating states, in contrast, polyphase current is provided by the converter.
In the following, the present invention is explained in greater detail on the basis of examples with reference to the following FIGURE.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.